Interpretive Summary: Chlorimuron is applied mid-season to control Florida beggarweed in peanut. Chlorimuron can be applied from 60 days after emergence (DAE) until 45 days before harvest. Peanut are more tolerant of chlorimuron applied mid-season than when applied early-season. However, Florida beggarweed are often too large for consistent control once peanut are old enough for treatment. It would be useful for peanut growers to apply chlorimuron earlier than 60 DAE and presumably to younger Florida beggarweed for more consistent control and protect peanut from weed competition. Trials were conducted to determine if the benefits of controlling smaller Florida beggarweed with chlorimuron applied earlier in the season compensate for increased risk of peanut injury. Chlorimuron (9 g ai/ha) was applied at 21, 35, 49, 63, 77, and 91 DAE. Additionally, flumioxazin (105 g ai/ha) PRE was included as a treated control, along with a nontreated control. Main plots were split into subplots; weed-free and weeds present. The only treatment that effectively controlled Florida beggarweed was flumioxazin PRE. Chlorimuron controlled Florida beggarweed 38 to 67%, with applications at 21 and 35 DAE more efficacious than chlorimuron applied later. With weeds present, peanut treated with chlorimuron at any time of application yielded less than peanut treated with flumioxazin PRE. Weed free peanut treated with chlorimuron at any time of application yielded less than peanut treated with flumioxazin PRE. These data indicate that chlorimuron can be applied earlier than 60 DAE and provide better Florida beggarweed control with greater peanut yields than when applied at the recommended time intervals. However, Florida beggarweed control and peanut yields from any of the chlorimuron treatments were consistently less than flumioxazin PRE.

Technical Abstract:
Chlorimuron is applied mid-season to control Florida beggarweed in peanut. Chlorimuron can be applied from 60 days after emergence (DAE) until 45 days prior to harvest. Trials were conducted in Georgia to determine if the benefits of controlling smaller Florida beggarweed with chlorimuron applied earlier in the season compensate for increased risk of peanut injury. Chlorimuron (9 g ai/ha) was applied at 21, 35, 49, 63, 77, and 91 DAE. Additionally, flumioxazin (105 g ai/ha) PRE was included as a treated control, along with a nontreated control. Main plots were split into subplots; weed-free and weeds present. The only treatment that effectively controlled Florida beggarweed was flumioxazin PRE. Chlorimuron controlled Florida beggarweed 38 to 67%, with applications at 21 and 35 DAE more efficacious than chlorimuron applied later. With weeds present, peanut treated with chlorimuron at any time of application yielded less than peanut treated with flumioxazin PRE. Weed free peanut treated with chlorimuron at any time of application yielded less than peanut treated with flumioxazin PRE. These data indicate that chlorimuron can be applied earlier than 60 DAE and provide better Florida beggarweed control with greater peanut yields than when applied at the recommended time intervals. However, Florida beggarweed control and peanut yields from any of the chlorimuron treatments were consistently less than flumioxazin PRE.